The invention relates to a waveguide plate and a process for its production and a microtitre plate comprising such a waveguide plate and as used, for example, for analytical purposes in the biochemical and medical sector.
U.S. Pat. No. 5,675,691 discloses a waveguide plate of the generic type, in which coupling gratings are produced by applying a waveguide layer comprising TiO2, Ta2O5, HfO2, Y2O3, Al2O3, Nb2O5, nitride or oxynitride of Al, Si or Hf to a substrate comprising glass, in particular quartz glass, ceramic or predominantly organic material, it being possible to provide a 20 nm thick intermediate layer, e.g. of SiO2, and to structure said waveguide layer by ablation or modification of the refractive index by means of exposure to two superposed beams of an excimer laser or to a beam modified by a mask. Instead, it is also possible to structure an intermediate layer, e.g. comprising TiO2, in which the ablation barrier is lower and which is applied either to the waveguide layer or directly to the substrate and, in the latter case, is superposed by the waveguide layer after structuring. The grating constants are, for example, 375 nm or 440 nm. The grating area is freely selectable and may be, for example, 1 mmxc3x971 mm or 8 mmxc3x978 mm.
U.S. Pat. No. 5,822,472 discloses a waveguide plate for chemical analyses which bears a 40 nm to 160 nm thick waveguide layer comprising TiO2, ZnO, Nb2O5, Ta2O5, HfO2 or ZrO2 on a carrier comprising plastic, glass or quartz. An intermediate layer comprising nonluminous material of low refractive index, e.g. quartz of, for example, 100 nm thickness, where it simultaneously serves as an adhesion promoter, may be arranged in between. An incoupling grating and an outcoupling grating are provided, which are created by known photolithographic or holographic and etching methods in the carrier or in the waveguide layer and have a grating constant of between 200 nm and 1000 nm. The grating may have dimensions of 2 mm (parallel lines)xc3x974 mm with a total area of the waveguide plate of 12 mmxc3x9720 mm.
J. Dxc3xcbendorfer and R. E. Kunz: xe2x80x9cCompact integrated optical immunosensor using replicated chirped grating coupler sensor chipsxe2x80x9d, Applied Optics, 37/10 (1.4.1998) discloses a waveguide plate comprising a polycarbonate carrier plate into which a modulated incoupling grating having a grating constant varying between 420 nm and 422.8 nm and an outcoupling grating having a grating constant varying between 595.1 nm and 600.8 nm were impressed. Thereafter, a TiO2 waveguide layer having a thickness of 137 nm and a refractive index of 2.346 was applied by means of low-temperature DC magnetron sputtering, and finally the waveguide plate was silanized. The incoupling angle is xe2x88x929.5xc2x0 and the outcoupling angle is 22.5xc2x0.
U.S. Pat. No. 5,738,825 describes a microtitre plate on whose underside a 20 nm to 1000 nm, preferably 30 nm to 500 nm, thick waveguide layer comprising TiO2, Ta2O5, HfO2, ZrO2, SiO2, Si3N4, Al2O3, Nb2O5, nitride or oxynitride of Al, Si or Hf is mounted and is covered by a plastics layer. Incoupling and outcoupling gratings are mounted underneath each cavity. The gratings have a grating constant between 330 nm and 1000 nm, in particular about 400 nm to 800 nm, and are produced by lithographic or mechanical methods.
CH-A-688 165 discloses a waveguide plate comprising a substrate of plastic, e.g. polycarbonate, whose surface was structured mechanically, by thermoforming or embossing or during injection moulding, in particular provided with a coupling grating, and carries a waveguide layer applied by a PVD method and comprising TiO2, Ta2O5, ZrO2, Al2O3, SiO2xe2x80x94TiO2, HfO2, Y2O3, Nb2O51, silicon nitride, oxynitride, SiOxNy, HfOxNy, AlOxNy, TiOxNy, MgF2 or CaF2. To reduce the evaporation losses, an approx. 20 nm thick intermediate layer applied to the substrate before the waveguide layer and comprising an inorganic dielectric material, such as SiO2, is provided and simultaneously serves as an adhesion promoter.
All waveguide plates described above are produced by processes with which no satisfactory uniformity of the coupling grating can be achieved, so that the coupling angle varies relatively widely. Consequently, the relative angle of the exposure unit and of the waveguide plate has to be optimized in a complicated manner in each step during use. Some of the processes described are also very complicated or do not permit very large quantities of constant quality.
EP-A-0 602 829 discloses a process for producing a grating structure on a substrate, for example for a DBR semiconductor laser, in which first a phase mask is produced and then the substrate, e.g. InP, is exposed at the Littrow angle through the phase mask. The exposure can be effected by means of an Hgxe2x80x94Xe arc lamp having a light source diameter of 0.25 mm, three lines around 365 nm wavelength being filtered out. The substrate is located close to the phase mask, i.e. at a distance of not more than 10 xcexcm.
To produce the phase mask, a quartz substrate is covered with three layers, a photoresist layer, a thin germanium layer and finally a layer of a resist sensitive to electron beams. The uppermost layer is then structured by inscribing by means of electron beams, developing the uppermost layer and removing the unexposed parts. The structure is transferred to the layers underneath by reactive ion etching, initially with CF3Br and then with O2, and finally to the quartz substrate itself by a further step of reactive ion etching, whereupon the residues of the layers are removed. The grating constant may be, for example, between 190 nm and 250 nm. The phase mask may be several centimeters long and the grating may extend over its entire length. However, the length of the lines is as a rule only 5-20 xcexcm. Greater lengths are possible but require very long processing times. In practice, gratings of more than 1 mm2 can scarcely be produced with reasonable effort and good accuracy. In particular, stitching errors during inscribing by means of electron beams cannot be avoided.
It is the object of the invention to provide a waveguide plate which permits feasible rapid analysis with little effort. In addition, it is intended to provide a microtitre plate based on such a waveguide plate. As a result of the limits which are narrow also with large grating lengths and within which the coupling angle varies, it is possible simultaneously to expose and to read out larger parts of the waveguide plate or microtitre plate. Successive exposures of different parts of the waveguide plate or microtitre plate are also simplified since reoptimization of the relative angle between it and the exposure unit is either not required or in any case is very easy.
Furthermore, it is the object of the invention to provide a process for producing a waveguide plate according to the invention, which permits the creation of large gratings in particular having long parallel lines with great precision, provides freedom of design with regard to the arrangement of the gratings and is simple and economical. The process according to the invention furthermore permits the production of large series of waveguide plates of constant quality and having optical properties, such as coupling efficiencies and in particular coupling angles, which are within narrow limits.